The present invention relates to the treatment of articles, particularly medical articles such as absorbable sutures, clips and staples, by subjecting them to a gaseous sterilizing agent to sterilize the products. The particular gaseous sterilizing agent employed is ethylene oxide which is a well known gas used as a sterilizing agent.
The present process is particularly useful in the sterilization of moisture sensitive medical products, that is, products that will degrade if exposed to atmospheric moisture. This type of product includes sutures, ligating clips and staples made from polymeric materials which will absorb over time in an animal or human body. These polymeric materials include homopolymer and copolymers of glycolide and lactide; polymers have dioxanone linkages, and copolymers of a dioxanone with other monomers such as caprolactone; and mixtures of such polymers and copolymers.
Generally, these polymers are very sensitive to moisture and are broken down in the body by a hydrolytic degradation or a combination of hydrolytic degradation and other activity. It is therefore necessary that products made from such polymers be packaged in air tight containers which are substantially impervious to water vapor including atmospheric moisture, to prevent the degradation of the product during storage. Generally, these packages are laminates which include one or more metallic foil layers. The atmospheric moisture cannot penetrate the metallic foil layer of the package and therefore these products have long term storage stability. Some of these absorbable polymers are also degraded by oxygen. The metal foil packaging materials also prevent oxygen from penetrating the package and contacting the product during storage. Medical products made from oxygen degradable polymers are usually packaged in a nitrogen or other inert gas atmosphere to limit degradation during storage.
An example of this type of a package that is commonly used such products is shown in U.S. Pat. No. 3,815,315 which discloses an absorbable suture material sterilized with an ethylene oxide containing gas and packaged in a package with a metallic foil layer.
The prior art sterilization process which is disclosed in U.S. Pat. No. 3,815,315 comprises placing the surgical product in a packaging material which is substantially impervious to moisture vapor. The package is sealed on three sides with the fourth side open to the atmosphere. This package is then placed in a bacteria proof transfer container which is permeable to the sterilizing gas but not permeable to bacteria. The transfer container holding the open suture package is then placed in a ethylene oxide sterilizing chamber. Ethylene oxide in combination with a fluorocarbon gas diluent or other diluent is added to the sterilizer. After sterilization is effected, the transfer container containing the open package is placed in a dryer and the product is dried under heat and vacuum, to remove any water from the suture. The transfer container is removed to a dry room where it is stored in a substantially moisture free atmosphere until the final sealing of the package. At that time, the transfer container is transferred to a sterile area the foil package containing the suture is removed from the transfer container and the gas is removed from the package and replaced with an anhydrous gas and the foil laminate is sealed. The foil package is then placed in an outer envelope which may be moisture previous and the space between the two envelopes is then sterilized to sterilize the outer surface of the inner metal foil package.
The above mentioned prior art process of sterilization employs an intermediate packaging step, the bacteria proof transfer container, to protect the sterility of the product from the point of sterilization to the point where the package is finally sealed. The foil package must be removed from the transfer container before it can be sealed. This step may introduce some contamination of the package or may introduce moisture into the package after the product has been dried.
Prior art sterilization techniques employing ethylene oxide generally use a single vessel or chamber which is put through successive steps of loading of the item to be sterilized, evacuation of the vessel, subjecting the item to be sterilized to a sterilizing gas for the required time period to effect the sterilization and the subsequent removal of the sterilizing gas from the vessel and subjecting the packaged product to out-gassing or a vacuum removal of the ethylene oxide from the package. Since ethylene oxide is a toxic material it is not desired in the finished product or package. Generally, packaged products are subjected to out gassing or aeration to remove the ethylene oxide from the package. Examples of ethylene oxide sterilization include the process as described in the above mentioned U.S. Pat. No. 3,815,315 as well as the process described in U.S. Pat. Nos. 3,068,864; 3,767,362 and 5,128,101. In addition to the steps mentioned above, there is also a step of humidifying the product to be sterilized prior to the contacting of the product with the sterilizing gas. In the situations where the product to be sterilized is not subject to degradation by water or oxygen, the package can be made from a material that allows passage of the sterilizing gas and air but prevents the passage of bacteria. Therefore, the package may be completely sealed and sterilized and then aerated without danger of the product being contaminated during processing.
Sterilization with ethylene oxide has also been carried out in separate unconnected vessels or chambers, for example; a preconditioning vessel, a sterilization vessel and an out gassing vessel. The product to be sterilized is physically moved through the ambient atmosphere from one vessel to the next vessel in the sterilization process. This type of sterilization has been employed for packages which are completely sealed prior to sterilization.
One of the problems with the use of ethylene oxide gas as a sterilizing agent is that mixtures of ethylene oxide and oxygen or air are explosive. Care must be exercised with ethylene oxide to avoid the possibility of inadvertently forming an explosive concentration of ethylene oxide in air. To reduce this possibility, ethylene oxide is usually employed as a sterilizing gas in a mixture with an inert gas such as a fluorocarbon, carbon dioxide and in some instances, nitrogen. A negative aspect of such lower concentration of ethylene oxide in sterilizing gas mixtures is that the sterilization time is generally extended as the concentration of the ethylene oxide is reduced.